CVE-2026-47857 Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around
Attackers can cause a stream hang and denial of service in Reactor Core applications using windowTimeout with fairBackpressure due to an index wrap-around.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47857?
CVE-2026-47857 is a medium-severity vulnerability in Spring Reactor Core, published on 26 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In Reactor Core, applications that use the Flux.windowTimeout operator with fairBackpressure enabled are vulnerable to a Denial of Service (DoS) condition. Reactor Core 3.8.0 - 3.8.6 Reactor Core 3.5.0 - 3.7.19 Reactor Core 3.4.41 and earlier
Weakness: CWE-190
Which versions are affected by CVE-2026-47857?
It affects 1 product.
Products include Broadcom Reactor Core.
How do I fix CVE-2026-47857?
Upgrade to a fixed version.
Is CVE-2026-47857 being exploited?
There is no known exploitation of CVE-2026-47857 in the wild and no public exploit code.
Other vulnerabilities in Spring Reactor Core
Sources
Also known as CLEANSTART-2026-AM40974, CLEANSTART-2026-OE47351, CLSA-2026-1791442790, CLSA-2026-1791455070, CLSA-2026-1791457895, CLSA-2026-1791972789 and 8 more.